1. Field of the Invention
The present invention relates to a process for forming a fine pattern in a semiconductor device to form a circuit pattern in an IC (integrated circuit), an LSI (large-scale integrated circuit), or the like.
2. Description of the Prior Art
The technique of forming a fine pattern in a semiconductor device are described in "Submicron Ryoiki niokeru Pattern Keisei Gijutsu (Techniques of forming Pattern in Submicron Order)," Okidenki Kenkyu Kaihatsu No. 133 (Okidenki Research and Development No. 133), Vol. 54, No. 1, Jan., pp. 85-86, 1987; J. Vac. Sci. Technol., 19-(4), Nov./Dec., pp. 1313-1319, 1981; etc.
As can be understood from these pieces of literature, the techniques of forming a fine pattern in an IC or an LSI include multiple-layer resist processes, in which a structure comprising different kinds of resist in laminate fashion is used to utilize an effect of planarizing a substrate and/or decreasing light reflection by the underlayer resist to thereby improve the resolution of the upperlayer resist in pattern formation therein, thus enabling a fine pattern to be formed.
The multiple-layer resist processes include a deep UV (hereinafter referred to as "deep ultraviolet light" when necessary) blanket exposure method and an RIE (refractive ion etching) method, which differ from each other in the way of transferring an upperlayer resist pattern to an underlayer resist.
Of them, the deep UV blanket exposure method uses as an underlayer resist a resist having a photosensitivity to deep UV light, and comprises the step of blanket exposure (exposure of a whole surface of a substrate-cum-resist to parallel light without use of a mask except for a resist used as a mask as mentioned below) to deep UV light with an upperlayer resist pattern being used as a mask to transfer the upperlayer resist pattern to the underlayer resist.
FIG. 1 illustrates a representative instance of a double-layer resist process which is carried out according to the deep UV blanket exposure method. The instance illustrated in FIG. 1 is an example of the double-layer resist process which is a technique disclosed in J. Vac. Sci. Technol., 19 (4), Nov./Dec., pp. 1313-1319, 1981, and in which a positive resist photosensitive to UV light (hereinafter referred to as "ultraviolet light" when necessary) is used as the upperlayer resist while a positive resist photosensitive to deep UV light is used as the underlayer resist.
First, an underlayer resist 2 [made of, for example, polymethyl methacrylate (PMMA), a copolymer of methyl methacrylate and methacrylic acid (P(MMA-MAA)), or polymethyl isopropenyl ketone (PMIPK)] as shown in FIG. 1b is formed on a Si substrate 1 as shown in FIG. 1a, followed by formation of an upperlayer resist 3 (made of, for example, AZ 1350, AZ 1450, Hunt HRP 206, Hunt MPR, Polychrome PC 129, or Kodak 809) as shown in FIG. 1c on the underlayer resist 2. When the upperlayer resist 3 is directly deposited on the underlayer resist 2, a mixed layer (hereinafter referred to as an "interfacial layer") is formed in the interface therebetween.
After the formation of the underlayer resist 2 and the upperlayer resist 3, the latter is subjected to photolithography comprising exposure to UV light 6 through a mask 5 as shown in FIG. 1d to form a pattern of the resist 3 as shown in FIG. 1e.
Subsequently, the exposed areas of the interfacial layer 4 are removed using oxygen plasma or a suitable method as shown in FIG. 1f.
Subsequently, the pattern of the upperlayer resist 3 is transferred to the underlayer resist 2 using deep UV light 7 with the pattern of the upperlayer resist 3 being used as a mask according to the deep UV blanket exposure method as shown in FIG. 1g.
Thereafter, the underlayer resist 2 is developed to obtain a final resist pattern as shown in FIG. 1h.
As is apparent from the above description, however, the above-mentioned process has defects in that the steps are complicated and hence it is inevitable that equipment of a complicated structure must be used in practicing the process, because two development operations be carried out.